U.S. patent application number 11/335746 was filed with the patent office on 2006-07-13 for traction control for downhole tractor.
Invention is credited to Falk W. Doering, Robin A. Ewan, Benoit A. Foubert, Todor K. Sheiretov.
Application Number | 20060151212 11/335746 |
Document ID | / |
Family ID | 34711465 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060151212 |
Kind Code |
A1 |
Doering; Falk W. ; et
al. |
July 13, 2006 |
Traction control for downhole tractor
Abstract
Apparatus, system and methods useful for controlling the
traction of a downhole tractor in a borehole include the capability
of repeatedly adjusting the normal force applied to at least one
component that causes movement of the tractor in the borehole.
Inventors: |
Doering; Falk W.; (Houston,
TX) ; Sheiretov; Todor K.; (Houston, TX) ;
Ewan; Robin A.; (Stafford, TX) ; Foubert; Benoit
A.; (Houston, TX) |
Correspondence
Address: |
SCHLUMBERGER CONVEYANCE AND DELIVERY;ATTN: ROBIN NAVA
555 INDUSTRIAL BOULEVARD, MD-1
SUGAR LAND
TX
77478
US
|
Family ID: |
34711465 |
Appl. No.: |
11/335746 |
Filed: |
January 19, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10751599 |
Jan 5, 2004 |
|
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11335746 |
Jan 19, 2006 |
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Current U.S.
Class: |
175/24 ;
175/99 |
Current CPC
Class: |
E21B 23/14 20130101;
E21B 4/18 20130101; E21B 23/001 20200501 |
Class at
Publication: |
175/024 ;
175/099 |
International
Class: |
E21B 44/00 20060101
E21B044/00; E21B 4/00 20060101 E21B004/00 |
Claims
1. An apparatus for adjusting the traction of a downhole tractor
moveable within a borehole, the apparatus comprising: at least one
drive module including at least one drive unit, said at least one
drive unit being engageable with and moveable relative to a wall of
the borehole, said at least one drive module being capable of
determining the velocity of the at least one drive unit in the
borehole, said at least one drive module being capable of applying
normal force to said at least one drive unit to cause said at least
one drive unit to engage and move with respect to the wall of the
borehole; and at least one measuring unit capable of determining
the velocity of the tractor in the borehole, whereby said at least
one drive module is capable of varying the normal force on said at
least one drive unit based upon the velocity of the tractor and the
velocity of said at least one drive unit.
2. The apparatus of claim 1 wherein said at least one measuring
unit is capable of determining the diameter of the borehole.
3. The apparatus of claim 2 furthering including at least two
measuring units, whereby the tractor is movable in opposite
directions in the borehole.
4. The apparatus of claim 1 wherein said at least one drive unit
determines the velocity of said at least one drive unit.
5. The apparatus of claim 1 wherein said at least one drive module
includes at least one normal force generator capable of applying
the normal force to said at least one drive unit, and at least one
normal force controller capable of causing said at least one normal
force generator to change the magnitude of said normal force
applied to said at least one drive unit.
6. The apparatus of claim 5 wherein said at least one normal force
controller repeatedly determines the actual slip of said at least
one drive unit relative to the borehole wall.
7. The apparatus of claim 6 wherein said at least one normal force
controller repeatedly determines if the slip of said at least one
drive unit is excessive and controls the dynamic application of
normal force to said at least one drive unit by said at least one
normal force generator.
8. The apparatus of claim 7 wherein said normal force controller
causes said at least one normal force generator to increase the
normal force applied to said at least one drive unit if the actual
slip of said at least one drive unit slip is excessive.
9. The apparatus of claim 8 wherein said normal force controller
causes said at least one normal force generator to decrease the
normal force applied to said at least one drive unit if the actual
slip of said at least one drive unit slip is below an acceptable
slip value.
10. The apparatus of claim 5 further including a main controller
capable of receiving signals from said at least one measuring unit
relating to at least one among the velocity of the tractor and the
diameter of the borehole.
11. The apparatus of claim 10 wherein said main controller is
capable of transmitting signals relating to the velocity of the
tractor from said at least one measuring unit to said at least one
normal force controller.
12. The apparatus of claim 11 wherein said main controller is
capable of transmitting signals relating to the borehole diameter
to said at least one normal force controller.
13. The apparatus of claim 11 wherein at least one among said main
controller and at least one said normal force controller is at
least partially mechanically actuated.
14. The apparatus of claim 11 wherein at least one among said main
controller and at least one said normal force controller is at
least partially hydraulically actuated.
15. The apparatus of claim 11 wherein at least one among said main
controller and at least one said normal force controller is at
least partially electronically actuated.
16. The apparatus of claim 15 wherein at least one among said main
controller and at least one said normal force controller includes
control logic.
17. The apparatus of claim 10 wherein said main controller is part
of another component of the apparatus.
18. The apparatus of claim 10 wherein at least part of at least one
among said main controller and said at least one measuring unit is
located at the surface.
19. The apparatus of claim 10 wherein said at least one drive unit
includes a drive unit speed control mechanism and is capable of
operating at a requested velocity.
20. A drive module useful for controlling the traction of a
downhole tractor in a borehole, the drive module comprising: at
least one drive unit engageable with and moveable relative to a
wall of the borehole to move the tractor through the borehole; at
least one normal force generator capable of applying a normal force
to said at least one drive unit to cause said at least one drive
unit to move relative to the borehole; and at least one normal
force controller in communication with said at least one normal
force generator, said at least one normal force controller being
capable of causing said at least one normal force generator to vary
the magnitude of the normal force applied to said at least one
drive unit based upon the slip of said at least one drive unit.
21. The drive module of claim 20 wherein said at least one normal
force controller repeatedly determines the slip of said at least
one drive unit and causes said at least one normal force generator
to vary the magnitude of the normal force applied to said at least
one drive unit on a continuous basis as long as movement of the
tractor in the borehole is desired.
22. The drive module of claim 21 wherein said normal force
controller causes said at least one normal force generator to
increase the normal force on said at least one drive unit if the
slip of said at least one drive unit is excessive and to decrease
the normal force on said at least one drive unit if the slip of
said at least one drive unit is below a minimum acceptable slip
value.
23. The drive module of claim 22 wherein said at least one drive
unit includes at least one sprocket wheel and at least one drive
chain, said at least one drive chain being engageable with the
borehole wall.
24. The drive module of claim 23 wherein said at least one normal
force generator includes at least one linear actuator engageable
with at least one said sprocket wheel, said at least one linear
actuator assisting in applying the normal force to said at least
one drive unit.
25. The drive module of claim 22 wherein said at least one drive
module includes at least one wheel engageabe with the borehole wall
and wherein said at least one normal force generator includes at
least one linear actuator engageable with at least one said wheel,
whereby said at least one linear actuator assists in applying the
normal force to said at least one drive unit.
26. The drive module of claim 22 wherein said at least one drive
module includes at least one grip assembly and wherein said at
least one normal force generator includes at least one linear
actuator engageable with said at least one grip assembly, whereby
said at least one linear actuator assists in applying the normal
force to said at least one drive unit.
27. An automated system useful for adjusting the traction of a
downhole tractor in a borehole, the traction created by applying
normal force to one or more member that is associated with the
tractor and engageable with the borehole wall, the system
comprising: at least two drive modules capable of generating and
applying the normal force to at least one member associated with
the tractor and moving the tractor through the borehole; at least
one measuring unit capable of repeatedly determining at least one
among the velocity of the tractor in the borehole and the diameter
of the borehole; and a main controller in communication with said
at least two drive modules and said at least one measuring unit,
and said at least one drive module being capable of varying the
magnitude of normal force required for moving the tractor through
the borehole based at least partially upon signals received from
said main controller.
28. The system of claim 27 wherein the tractor has first and second
ends, further including a first said measuring unit disposed
proximate to the first end of the tractor and a second said
measuring unit disposed proximate to the second end of the
tractor.
29. The system of claim 28 further including a cable connected with
the tractor for communication with the surface.
30. The system of claim 28 further including at least one conveyed
tool connected with the tractor for delivery by the tractor into
the borehole.
31. The system of claim 30 wherein at least one said conveyed tool
is located between components of the tractor.
32. The system of claim 28 wherein each said at least two drive
modules includes at least one drive unit, further including at
least one force transducer capable of providing information about
the load applied to at least one said drive unit.
33. The system of claim 32 further including at least one force
sharing module capable of balancing the load distribution among
said at least two drive units.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to apparatus, systems and methods for
controlling or adjusting the traction of a downhole tractor in a
borehole.
[0002] In the petroleum exploration and production industries,
downhole tractors are often used to convey tools and other devices
into boreholes. However, downhole tractors may be used for any
desired purpose. As used throughout this patent, the terms
"tractor", "downhole tractor" and variations thereof means a
powered device of any form, configuration and components capable of
crawling or moving within a borehole. The term "borehole" and
variations thereof means and includes any underground hole,
passageway or area. An "open borehole" is a borehole that does not
have a casing. A "non-vertical borehole" is a borehole that is at
least partially not vertically oriented, such as a horizontal or
deviated well.
[0003] Typically, the movement of the tractor is enabled by
friction-generated traction between one or more component
associated with the tractor, referred to herein as the "drive
unit(s)," and the borehole wall. In such instances, a normal force
is usually applied to the drive unit to press it against the
borehole wall.
[0004] For a tractor to achieve or maintain movement within a
borehole, the drive unit cannot completely slip relative to the
borehole wall, so that the traction force
(F.sub.T).ltoreq..mu.F.sub.N, where .mu. is the friction
coefficient between the drive unit and the borehole wall and
F.sub.N is the normal force. Also, the drive unit must provide
enough traction force to overcome drag or resistance (F.sub.R) on
the drive unit, such as may be caused by the conveyed tool(s) and
delivery cable, so that F.sub.T.gtoreq.F.sub.R.
[0005] Any number of other factors (referred to throughout this
patent as "disturbance factors") may affect the amount of traction
necessary to move the tractor within the borehole in any particular
situation and environment of operation. For example, when the
borehole wall possesses an irregular surface, the amount of
traction necessary for movement and/or the coefficient of friction
may change as the borehole surface navigated by the tractor
changes. A few other examples of disturbance factors that may
affect the tractor's resistance to motion are changes in the
inclination of the borehole, diameter of the borehole, surface of
the borehole, borehole wall properties, increasing cable drag (when
a cable is used), debris in the borehole and borehole fluid
properties.
[0006] When the amount of traction needed for the tractor to move
or continue moving in the borehole changes, the normal force on the
drive unit(s) must be adjusted. Otherwise, the tractor may
experience excessive slippage. Hence, in order to keep
F.sub.T.ltoreq..mu.F.sub.N, the normal force F.sub.N has to be
adjusted. The normal force may also need to be adjusted when it is
desired to prevent power overload or unnecessary excessive normal
force. Thus, although not essential for tractor operations (or the
present invention), an ideal value for the normal force is
F.sub.N=F.sub.T/.mu., particularly when the tractor is moving in an
open, non-vertical or highly deviated borehole.
[0007] If the borehole conditions change infrequently and there are
no substantial tractor disturbance factors, such as may exist in a
"cased" borehole, the normal force may be effectively adjusted by
an operator sending commands to the tractor from the surface using
existing technology. However, when the amount of needed traction
changes often, such as in an open borehole or because of the
existence of disturbance factors, the operator is unlikely to react
sufficiently, often or quickly enough, resulting in excessive
slippage and, thus, poor tractor performance, and/or excessive
power to the drive units. Examples of existing downhole tractor
technology not believed to provide sufficient or efficient traction
control in such instances are disclosed in U.S. Pat. No. 6,089,323
issued on Jul. 18, 2000 to Newman et al. and U.S. Pat. No.
5,184,676 issued on Feb. 9, 1993 to Graham et al. Examples of
existing traction control technology for entirely different
applications not involving downhole tractors are U.S. Pat. No.
6,387,009B1 to Haka and issued on May 14, 2002 and German Patent DE
19,718,515 to Bellgardt and issued on Mar. 26, 1998. Each of the
above-referenced patents is hereby incorporated by reference herein
in its entirety.
[0008] Thus, there remains a need for methods, apparatus and/or
systems that are useful with downhole tractors and have one or more
of the following attributes, capabilities or features: adjusting
the normal force on one or more drive unit continuously,
automatically, without human intervention, on a real-time basis, or
any combination thereof; optimizing the traction of the drive
unit(s) in the borehole by adjusting or controlling the normal
force; applying as much normal force as necessary to reduce
slippage and as little normal force as necessary to minimize waste
of available power; adjusting the normal force as quickly as
possible without the necessity of human involvement; reacting to or
dealing with typical disturbance factors by adjusting the normal
force on the drive unit(s); real-time adjustment of normal forces
on the drive unit(s) to maintain or cause movement of the tractor
in the borehole; allowing the tractor to achieve continuous motion,
as may be desired or required in downhole data logging
applications, at the lowest effective normal force; preventing
excessive or unnecessary wear on components, loss of energy and
casing or formation damage caused by excessive normal forces.
BRIEF SUMMARY OF THE INVENTION
[0009] Various embodiments of the invention involve a method of
controlling the traction of a downhole tractor in a borehole, the
traction created by applying normal force to at least one drive
unit associated with the tractor, the method including repeatedly
determining the slip of the at least one drive unit, repeatedly
determining if the slip is excessive, and if the slip is excessive,
increasing the normal force on the at least one drive unit.
[0010] In other embodiments, instead of increasing the normal force
when slip is excessive, the normal force on the at least one drive
unit is decreased if the slip is below a minimum acceptable level.
In yet other embodiments, both the increasing and decreasing
options are included.
[0011] Some embodiments of the present invention include a method
of adjusting the traction of a downhole tractor in a borehole, the
method including measuring the velocity of drive unit(s), measuring
the velocity of the tractor, determining the slip of the drive
unit(s) based upon the velocity of the drive unit(s) and the
velocity of the tractor and comparing the slip of the drive unit(s)
to an acceptable slip value or range to determine if the slip of
the drive unit(s) is excessive. If the slip of the drive unit(s) is
excessive, the normal force on the drive unit(s) is increased.
[0012] In many embodiments of the present invention, a method of
real-time, dynamic adjustment of the traction of a downhole tractor
in a borehole without human intervention includes increasing the
normal force on at least one drive unit when the slip of the drive
unit(s) relative to the borehole wall is excessive and decreasing
the normal force on the drive unit(s) when the slip is below a
minimum acceptable level.
[0013] There are embodiments of the invention that involve a method
of real-time, dynamic adjustment of the traction of a downhole
tractor in a borehole without human intervention, the method
including changing the normal force applied to at least one drive
unit in response to a suitable change in at least one among the
diameter of the borehole, the presence of debris in the borehole,
one or more borehole fluid property, the surface of the borehole,
the inclination of the borehole, one or more borehole wall
property, the actual slip of the at least one drive unit relative
to the borehole wall, the coefficient of friction between the at
least one drive unit and the borehole wall, and the drag created by
a cable connected with the tractor.
[0014] The present invention may be embodied in a method of
optimizing the amount of energy required for maintaining the
movement of a downhole tractor within a borehole without human
intervention, the method including automatically, dynamically
adjusting the normal force applied to at least one drive unit in
response to changes in the actual slip of the at least one drive
unit relative to the borehole wall as compared to an acceptable
slip value or range.
[0015] Yet various embodiments involve a method of optimizing the
amount of energy required for maintaining the movement of a
downhole tractor within a borehole, the method including
automatically changing the normal force applied to at least one
drive unit without human intervention in response to one or more
change in at least one among the diameter of the borehole, the
presence of debris in the borehole, one or more borehole fluid
property, the surface of the borehole, the inclination of the
borehole, one or more borehole wall property, the actual slip of
the drive unit relative to the borehole wall, the coefficient of
friction between the drive unit and the borehole wall, and the drag
created by a cable connected with the tractor.
[0016] Various embodiments of the invention involve an apparatus
for adjusting the traction of a downhole tractor that is moveable
within a borehole and which includes at least one drive module. The
drive module includes at least one drive unit that is engageable
with and moveable relative to a wall of the borehole. At least one
measuring unit is capable of determining the velocity of the
tractor in the borehole. Each drive module is capable of
determining the velocity of at least one drive unit in the borehole
and applying normal force to such drive unit(s) to cause it to
engage and move with respect to the borehole wall. Each drive
module is also capable of varying the normal force on the at least
one drive unit based upon the velocity of the tractor and the
velocity of the drive unit.
[0017] Some embodiments involve a drive module useful for
controlling the traction of a downhole tractor in a borehole. The
drive module includes: at least one drive unit engageable with and
moveable relative to a wall of the borehole to move the tractor
through the borehole; at least one normal force generator capable
of applying a normal force to at least one drive unit to cause the
drive unit to move relative to the borehole; and at least one
normal force controller in communication with the at least one
normal force generator and capable of causing the normal force
generator to vary the magnitude of the normal force applied to at
least one drive unit based upon the slip of the drive unit.
[0018] The present invention may be embodied in a system useful for
adjusting the traction of a downhole tractor in a borehole that
includes at least two drive modules capable of generating and
applying a normal force and moving the tractor through the
borehole. At least one measuring unit is capable of repeatedly
determining at least one among the velocity of the tractor in the
borehole and the diameter of the borehole. A main controller is in
communication with the drive modules and the measuring unit. Each
drive module is capable of varying the magnitude of normal force
required for moving the tractor through the borehole based at least
partially upon signals received from the main controller.
[0019] Accordingly, the present invention includes features and
advantages which are believed to enable it to advance downhole
tractor technology. Characteristics and advantages of the present
invention described above and additional features and benefits will
be readily apparent to those skilled in the art upon consideration
of the following detailed description of preferred embodiments and
referring to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] For a detailed description of preferred embodiments of the
invention, reference will now be made to the accompanying drawings
wherein:
[0021] FIG. 1 is partial block diagram of a downhole tractor
equipped with an embodiment of a traction control system in
accordance with the present invention;
[0022] FIG. 2 is a block diagram showing various example inputs,
outputs and disturbance factors of the exemplary tractor of FIG.
1;
[0023] FIG. 3 is a flow diagram illustrating the process of an
embodiment of a method of adjusting traction in accordance with the
present invention;
[0024] FIG. 4 is a flow diagram illustrating the process of another
embodiment of a method of adjusting traction in accordance with the
present invention;
[0025] FIG. 5 is a generalized representation in partial block
diagram of an embodiment of a tractor velocity measuring unit in
accordance with the present invention deployed in a borehole;
[0026] FIG. 6 is a partial block diagram of an embodiment of a
measuring unit in accordance with the present invention deployed in
a borehole;
[0027] FIG. 7 is a partial block diagram of another embodiment of a
measuring unit in accordance with the present invention deployed in
a borehole;
[0028] FIG. 8 is a partial block diagram of still another
embodiment of a measuring unit in accordance with the present
invention deployed in a borehole;
[0029] FIG. 9 is a generalized representation in partial block
diagram of an embodiment of a drive module in accordance with the
present invention deployed in a borehole;
[0030] FIG. 10 is a partial block diagram of an embodiment of a
drive module in accordance with the present invention deployed in a
borehole;
[0031] FIG. 11 is a partial block diagram of another embodiment of
a drive module in accordance with the present invention deployed in
a borehole;
[0032] FIG. 12 is a partial block diagram of yet another embodiment
of a drive module in accordance with the present invention deployed
in a borehole;
[0033] FIG. 13 is partial block diagram of a bidirectional downhole
tractor equipped with an embodiment of a traction control system
having at least three drive modules in accordance with the present
invention;
[0034] FIG. 14 is a flow diagram illustrating inputs and outputs of
various components of an embodiment of a traction control system in
accordance with the present invention; and
[0035] FIG. 15 is a flow diagram illustrating inputs and outputs of
the inner modular structure of an embodiment of a main controller
in accordance with the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0036] Presently preferred embodiments of the invention are shown
in the above-identified figures and described in detail below. It
should be understood that the appended drawings and description
herein are of preferred embodiments and are not intended to limit
the invention or the appended claims. On the contrary, the
intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims. In showing and describing the
preferred embodiments, like or identical reference numerals are
used to identify common or similar elements. The figures are not
necessarily to scale and certain features and certain views of the
figures may be shown exaggerated in scale or in schematic in the
interest of clarity and conciseness.
[0037] As used herein and throughout all the various portions (and
headings) of this patent, the terms "invention", "present
invention" and variations thereof are not intended to mean the
claimed invention of any particular appended claim or claims, or
all of the appended claims. The subject or topic of each such
reference is thus not necessarily part of, or required by, any
particular claim(s) merely because of such reference.
[0038] Referring initially to FIG. 1, an embodiment of a downhole
tractor 12 equipped with an exemplary traction control system 13 of
the present invention is shown in partial block diagram format
deployed in a borehole 10. The illustrated tractor 12 includes a
main controller 14, multiple drive modules 16 and a measuring unit
22. The drive modules 16 each include at least one drive unit (not
shown) and displace, or move, the tractor 12 and any attached
devices, such as one or more conveyed tool 30, through the borehole
10. The conveyed tools 30 are shown located forward of the tractor
12 and traction control system 13 with respect to the direction of
movement 11 of the tractor 12 in the borehole 10. However, the
conveyed tools 30 or other devices may be located rearward of or
adjacent to the tractor 12, or sandwiched between different
components of the tractor 12 and/or traction control system 13, or
a combination thereof. Moreover, the inclusion of conveyed tools or
other devices is not required.
[0039] Still referring to FIG. 1, the measuring unit 22 of this
embodiment determines the speed of the tractor 12 in the borehole
10. If desired, the measuring unit 22 may instead or also measure
other information, such as the diameter (D) of the borehole 10,
rugosity, etc. Data and commands may be exchanged between the main
controller 14 and the drive modules 16 and measuring unit 22 via a
data bus 24. The main controller 14 may communicate with the
surface (not shown) and vise versa through a cable 26 and user
interface 28. For example, data or commands (e.g., requested
initial tractor speed) may be sent from an operator or device at
the surface to the main controller 14, and information (e.g., the
number of active drive units) may be sent from the main controller
14 to the surface. Various data flow paths of this embodiment are
generally indicated with arrows 29.
[0040] The main controller 14, drive modules 16, measuring unit 22
and other exemplary components may be of any desired type and
configuration. Moreover, the particular components and
configuration of FIG. 1 are neither required for, nor limiting
upon, the present invention. For example, while three drive modules
16 and one measuring unit 22 are shown, the tractor 12 may include
any quantity of drive modules and measuring units. For another
example, the main controller 14 and measuring unit 22, while shown
located within the tractor 12, may instead be located at the
surface 12 or within the cable 26 or another component. Further,
any among the main controller 14, drive module(s) 16, measuring
unit 22, data bus 24, cable 26 and cable interface 28 may not be
distinct components, but instead their functionality performed by,
incorporated or integrated into, one or more other part or
component. The "drive module", for example, may not be a distinct
module, but may be any configuration of components capable of
generating and applying the normal force to a component to move the
tractor in the borehole.
[0041] Now referring to FIG. 2, the tractor 12 of the embodiment of
FIG. 1 has various inputs, outputs and disturbance factors. Example
inputs include energy 120 and requested tractor speed settings 122.
The energy may be electric or hydraulic power or any other desired,
suitable form of energy capable of sufficiently powering the
tractor and/or traction control system. Some example potential
outputs include tractor velocity 130, traction force 132, normal
force applied to the drive unit(s) 134 and dissipated heat 136.
Some example disturbance factors that may act upon the tractor 12
in the borehole, influence its traction and thus hinder its ability
to move effectively through the borehole are borehole size
restrictions 124, borehole inclination 126 and changes in the
coefficient of friction 128. However, these particular inputs,
outputs and disturbance factors are neither required by, nor
limiting upon, the present invention.
[0042] In accordance with the present invention, the normal force
on the drive unit(s) is adjusted, if necessary, as the tractor
moves through the borehole to establish or maintain traction, or to
achieve or maintain a particular tractor velocity. In accordance
with one embodiment of the invention, referring to the flow diagram
of FIG. 3, when the downhole tractor (not shown) is deployed in the
borehole, a value for the actual slip S.sub.A of the drive unit(s)
is obtained (step 140). The actual slip S.sub.A may be detected or
determined in any desirable manner. In some embodiments, for
example, the actual velocity V.sub.1 of the drive unit(s) and the
actual velocity V.sub.2 of the tractor are determined, and the slip
S.sub.A calculated based upon the formula
S.sub.A=(V.sub.1-V.sub.2)/V.sub.1. For another example, the actual
slip S.sub.A may be detected based upon the formula
S.sub.A=V.sub.1-V.sub.2.
[0043] Still referring to the embodiment of FIG. 3, the slip value
for the drive unit(s) of this example is then evaluated to
determine if it is excessive (step 142). For example, the actual
slip S.sub.A may be compared to an optimal, desired or acceptable
value or range of slip S.sub.O (the "acceptable slip"). The
acceptable slip S.sub.O may be provided, or detected in any
desirable manner. For example, in one embodiment, the acceptable
slip will occur when the derivative of .eta. with respect to s
(d.sub..eta./d.sub.s)=0, where .eta.=(Force)(V.sub.2)/Input Power.
If the drive unit is electric, for example, "Force" and "Input
Power" may be calculated based upon the torque or load cell,
current and voltage of the respective drive unit. If the slip
S.sub.A of a drive unit is excessive, the normal force F.sub.N on
that drive unit(s) is increased (step 148). The above process is
repeated on a continuing basis and the normal force F.sub.N applied
to the drive unit(s) automatically increased each time excessive
slip is found (so long as tractor movement in the borehole is
desired). If desired, this methodology may be repeated on a
"real-time" basis. As used herein and in the appended claims, the
term "real-time" and variations thereof means actual real-time,
nearly real-time or frequently. As used herein and in the appended
claims, the term "automatic" and variations thereof means the
capability of accomplishing the relevant task(s) without human
involvement or intervention. The frequency of repetition of this
process may be set, or varied, as is desired. For example, the
frequency of repetition may be established or changed based upon
the particular borehole conditions or type, or one or more
disturbance factor.
[0044] In some embodiments, if desired, the normal force F.sub.N on
the drive unit(s) may instead or also be adjusted in an effort to
optimize energy usage, prevent excessive increases of the normal
force(s), maintain a constant tractor velocity, or for any other
desired reason. For example, in the embodiment diagramed in FIG. 4,
the slip S.sub.A is determined and compared to an acceptable slip
range (step 141). If the actual slip S.sub.A is within the
acceptable slip range, the repeats continuously as desired.
Whenever the slip S.sub.A is outside the acceptable slip range, the
Slip S.sub.A is compared to a maximum slip value (step 142). If the
slip S.sub.A is above the maximum slip value (excessive slip), the
normal force F.sub.N on that drive unit(s) is increased (step 148).
If not (the slip S.sub.A is below the acceptable slip range), the
normal force F.sub.N on that drive unit(s) is decreased (step 146).
In the embodiment of FIG. 4, the normal force F.sub.N is thus
dynamically, automatically adjusted to apply only as much normal
force F.sub.N as is necessary. In other embodiments (not shown),
there may be circumstances where it is desirable to optimize energy
usage by decreasing the normal force when actual slip S.sub.A is
below an acceptable slip value or range, but not to increase normal
force when slip is excessive.
[0045] Any suitable control, communication, measuring and drive
components and techniques may be used with any type of downhole
tractor to perform the traction control methodology of the present
invention.
[0046] FIG. 5 is a generalized representation of an embodiment of
the measuring unit 22 in partial block diagram format disposed in a
borehole 10. The measuring unit 22 may be positioned as is desired.
For example, the measuring unit 22 may be aligned with the drive
units (not shown), positioned lengthwise, included within or
separate from the tractor 12 or a tool string 31, or a combination
thereof. If the measuring unit 22 is located forward of the drive
unit(s) 16 relative to the direction of movement 11 of the tractor
12 in the borehole 10 (see e.g. FIG. 1), information obtained by
the measuring unit 22 such as, for example, borehole diameter, may
be used in determining normal force adjustment in anticipation of
the drive unit's upcoming borehole conditions. Further, multiple
measuring units 22 may be desirable in various instances, such as
for bidirectional tractoring.
[0047] Still referring to the "black box" representation of FIG. 5,
the illustrated measuring unit 22 includes a pair of velocimeters
82 capable of measuring the velocity of the tractor 12. While two
velocimeters 82 are shown, any number may be included. This
embodiment also includes an optional well size detector 84 capable
of measuring the diameter of the borehole 10. A measuring unit
conditioner 80 is shown receiving and processing data from the
velocimeters 82 (and well size detector 84) and communicating data
to the main controller 14.
[0048] FIGS. 6-8 show some examples of particular types of
measuring units 22 in partial block diagram format disposed in a
borehole 10. In the embodiment of FIG. 6, the measuring unit 22
includes a pair of idlers 86, angle sensors 88, 90 and a computing
unit 92. Such a dual system allows slippage correction and
calculation of well diameter; however, any number of one or more
idler 86 and angle sensor 88, 90 may be used. The idlers 86 of this
example are mounted on spring biased idler rods 114 to bias them
outwardly against the borehole wall 10a and prevent excessive
slippage of the idlers 86. The angle sensors 88, 90 detect the
angle between the tractor 12 and the rods 114, and the idlers 86
measure their own rotational speed in the borehole 10. The
computing unit 92 calculates the actual tractor velocity and, if
desired, the borehole diameter based upon the length of the rods
114 and the angles .DELTA..sub.1 and .DELTA..sub.2.
[0049] In the embodiment of FIG. 7, the tractor speed and, if
desired, the borehole diameter are determined by using the Doppler
effect. This embodiment includes a Doppler effect computing unit
94, a sending unit 96 and a receiving unit 98. The sending unit 96
sends beams 100 continuously at a certain frequency to the borehole
wall 10a. The beams reflect back from the borehole wall 10a to the
receiving unit 98 at a certain angle E 102. The beams 100 can be of
any suitable type, such as, for example, electromagnetic or
acoustic beams. The Doppler effect computing unit 94 computes the
tractor speed based upon the frequency difference. If desired, the
computing unit 94 may also compute the borehole diameter based upon
the angle E 102. An example of the components and methodology that
may be used to measure velocity based upon the Doppler effect are
shown and described in U.S. Pat. No. 6,445,337 issued on Sep. 3,
2002 to Reiche, which is hereby incorporated by reference herein in
its entirety.
[0050] FIG. 8 shows an embodiment of the measuring unit 22 that
includes an accelerometer 104 and an integrator 106. The
accelerometer 104 continuously measures the acceleration of the
tractor 12, which information is integrated by the integrator 106
to determine tractor velocity.
[0051] Referring now to FIG. 9, a generalized representation of an
embodiment of a drive module 16 is shown in partial block diagram
format deployed in a borehole 10. The illustrated drive module 16
includes two drive units 36, each pressed by a normal force
generator 38 against the borehole wall 10a at an interface 37. The
normal force generator 38 may be any suitable device, such as an
electrically, hydraulically, spring or mechanically actuated
device. It should be understood that the drive module 16 does not
require two drive units 36, but may include any desired number of
one or more drive unit 36.
[0052] In this example, the normal force generator 38 is controlled
by a normal force controller 40, which repeatedly determines slip
of the corresponding drive units 36, such as described above.
Whenever the slip is excessive, the controller 40 causes the normal
force generator 38 to increase the normal force on the drive
unit(s) 36 until the slip is deemed not excessive by the controller
40. Also, if desired, when the slip falls below a minimum
acceptable level, the normal force controller 40 can be designed to
cause the normal force generator 38 to decrease the normal force on
the drive unit(s) 36 until the slip is determined by the controller
40 to be acceptable. This process continues so long as efficient
tractor movement in the borehole is desired. The normal force
controller 40 of this embodiment thus controls the dynamic
application of normal force to the drive unit(s) 36 by the normal
force generator 38.
[0053] One or more force transducer 42 is also included in this
example to provide information about the traction force of each
drive unit 36. This information may be used for any desired
purpose, such as to assist in sharing the load among multiple drive
units. However, transducers and load sharing among multiple drive
units are not required.
[0054] Still referring to the "black box" representation of FIG. 9,
various potential data flow paths between components of this
embodiment are generally indicated with arrows 29. For example, the
normal force controller 40 is shown receiving the drive unit
velocity (V.sub.1) from the drive units 36 and the tractor velocity
(V.sub.2) from the main controller 14 for its determination of
actual drive unit slip (S.sub.A). The normal force controller 40 is
shown providing the normal force generator 38 with commands for the
application or removal of normal force to the drive units 36.
[0055] For some optional examples, the drive units 36 provide drive
unit torque to the main controller 14 for determining load sharing,
providing information about bore hole conditions or any other
suitable purpose. The drive units 36 may be equipped with internal
speed control mechanisms and may receive requested speed settings
through the main controller 14 from an operator or other source. In
another optional example, the main controller 14 is shown providing
borehole diameter data to the normal force controller 40 for
determining the magnitude of normal force to be applied to the
drive units 36. For example, the normal force may be reduced in
anticipation of an upcoming well restriction. However, other or
different data may be exchanged between various components. The
above examples of data flow are neither required by, nor limiting
upon, the present invention.
[0056] FIGS. 10-12 illustrate various particular embodiments of the
drive module 16 in partial block diagram format disposed in a
borehole 10. In the example of FIG. 10, the drive unit 36 includes
a drive motor 54, a transmission 56 and multiple sprocket wheels
64. The transmission 56 has a transmission wheel 58, transmission
chain 60 and arm 62, which drive the sprocket wheels 64. The
sprocket wheels 64 move a drive chain 66, which contacts the
borehole wall 10a, transmits drive torque from the drive motor 54
to the wall 10a and displaces the tractor 12.
[0057] Still referring to FIG. 10, the normal force generator 38 of
this embodiment includes a normal force motor 44 and a linear
actuator 46. The linear actuator 46 may be mechanical,
electromagnetic, hydraulic or any other suitable type. If desired,
the linear actuator may be equipped with a suspension element 52
and a load measuring device 50, such as a load cell. An arm 62
extends between the end 112 of the linear actuator 46 and the
sprocket wheel(s) 64.
[0058] The linear actuator 46 converts rotary motion of the normal
force motor 54 to linear motion. The linear force generated by the
linear actuator 46 is converted into the normal force that presses
the drive chain 66 against the borehole wall 10a. This force
conversion takes place at a pin, or joint, 110 disposed at the
front end 112 of the linear actuator 46 and which is slidable
within a slot 108 in the drive module 16. Thus, increasing the
linear force generated by the normal force generator 38 moves the
joint 110 forward in the slot 108, decreasing the normal force
applied to the sprocket wheels 64. Likewise, the normal force will
be increased when linear force applied to the joint 110 is
decreased.
[0059] Now referring to the embodiment of FIG. 11, the drive unit
36 is generally the same as the drive unit 36 of the embodiment of
FIG. 10, except with respect to that portion that engages the
borehole wall 10a. In this example, at least one drive wheel 68 is
driven by the transmission chain 60 and arm 62 and engages the
borehole wall 10a to displace the tractor 12. When multiple drive
wheels 68 are included, drive torque may be transmitted to the
drive wheels 68 by gears 70 located between the drive wheels 68.
The normal force generator 38 of this example operates similarly as
that shown and described with respect to FIG. 10, but, in this
instance, with respect to the drive wheels 68.
[0060] In the embodiment of FIG. 12, the drive module 16 includes a
grip assembly 72 that is movable forward and rearward on a shaft 76
driven by a drive motor 54 and a linear actuator 78 located within
the shaft 76. The shaft 76 reciprocates between a power stroke and
a return stroke. The grip assembly 72 includes at least one
gripping pad 74 that engages and slides along the borehole wall
10a. The use of grip-type technology for moving downhole tractors
is disclosed in U.S. Pat. No. 6,179,055 issued on Jan. 30, 2001 to
Sallwasser et al., which is hereby incorporated by reference herein
in its entirety.
[0061] The normal force generator 38 of this embodiment is
generally the same as that described above with respect to FIG. 10.
However, instead of exerting a continuous normal force on sprocket
wheels, the normal force applied to the gripping pad 74 of this
embodiment alternates. During the power stroke of the shaft 76, the
grip embodiment 72 and gripping pad 74 are stationary relative to
the borehole 10. Consequently, the normal force applied to the
gripping pad 74 by the normal force generator 38 must be sufficient
enough to overcome loss of traction. During the return stroke of
the shaft 76, no normal force may be desired, such as to reduce
resistance and avoid component wear.
[0062] Now referring to FIG. 13, an embodiment of a bidirectional
downhole tractor 12 equipped with an exemplary traction control
system 13 of the present invention is shown in partial block
diagram format deployed in a borehole 10. The tractor 12 includes
at least three drive modules 16 (drive module.sub.1, drive
module.sub.2, drive modulen), each similar to the drive module 16
described above with respect to FIG. 9. A measuring unit 22,
similar to that described above with respect to FIG. 5, is included
at each end of the tractor 12. The main controller 14 communicates
with the various tension control system components via the data bus
24. A cable 26 and cable tension sensor 27 allow communication
between the main controller 14 and the surface (not shown). The
main controller 14, normal force controller 40 and measuring unit
conditioner 80 may be electronic, mechanical, hydraulic or driven
by any other suitable technology or technique, or a combination
thereof.
[0063] Still referring to the embodiment of FIG. 13, multiple
(optional) force transducers 42 are included for measuring and
comparing the traction force of the various drive units 36. The
force comparison data (F.sub.comparison) is communicated to the
main controller 14 for any desired use, such as to share load among
the drive units to improve efficiency. Also, multiple conveyed
devices, or tools, 30 are shown disposed between the drive modules
16 and at the forward end of the tractor 12 in the illustrated tool
string 31.
[0064] The flow diagram of FIG. 14 shows example input and outputs
of various components of an embodiment of a downhole tractor
traction control system 13 for use in a borehole (not shown) in
accordance with the present invention. Each (one or more) drive
module 16 includes a drive unit 36, normal force generator 38 and
normal force controller 40. Various measuring instruments, such as
a cable tension measurement device 27, traction force measurement
device 116, well size detector 84 and tractor speed measuring unit
22, provide information, such as cable tension, traction force,
borehole diameter (D.sub.1) and tractor speed (V.sub.2),
respectively, on an ongoing or repeating basis to the main
controller 14 and the user interface 28.
[0065] The main controller 14 communicates with the operator, or
surface, at a user interface 28. Various information may be
exchanged between the main controller 14 and user interface 28. For
example, commands, such as a requested drive unit velocity
(V.sub.1), may be provided from the user interface 28 to the main
controller 14. The main controller 14 of this embodiment may honor
or suppress such commands based upon one or more condition or
circumstance. If a requested drive unit velocity (V.sub.1) is
honored by the main controller 14, the controller 14 will pass the
command on to the individual drive units 36. If desired, this
request may be made only at the start of operations or at certain
times during operations. The main controller 14 may provide
additional information, such as maximum allowable torque, to each
drive unit 36.
[0066] The main controller 14 notifies each normal force controller
40 of the tractor velocity (V.sub.2) and pertinent borehole
diameter (D.sub.1). Each normal force controller 40 gives the
commands to its corresponding normal force generator 38 to apply
the desired normal force to the respective drive unit 36. The
normal force controllers 40 also provide a checkback signal to the
main controller 14. The checkback signal may be used by the main
controller 14 for logging information, such as the actual friction
factor. Also, in this example, each drive unit 36 notifies the main
controller 14 of its actual torque. It should be understood,
however, that each of the above exemplary inputs, outputs and data
communications is not required.
[0067] Additional components, capabilities and/or features may be
included in the traction control system of the present invention to
provide additional functions. For example, referring to FIG. 15, an
embodiment of the main controller 14 is shown including a surface
interface 150, well size calculator 32 and force sharing module 34.
The surface interface 150 communicates with the user interface 28.
The well size calculator 32 calculates borehole diameter based upon
measurements from a borehole size detector (not shown). The force
sharing module 34 balances the load distribution among multiple
drive units 36. This feature may desirable, for example, to improve
the ability of the tractor to overcome various obstacles, such as
washouts, borehole restrictions and obstructions. The exemplary
force sharing module 34 requires checkback signals representing
force values measured by transducers (not shown) and cable tension
values.
[0068] Preferred embodiments of the present invention thus offer
advantages over the prior art and are well adapted to carry out one
or more of the objects of the invention. However, the present
invention does not require each of the components and acts
described above, and is in no way limited to the above-described
embodiments and methods of operation. Further, the methods
described above and any other methods which may fall within the
scope of any of the appended claims can be performed in any desired
suitable order and are not necessarily limited to the sequence
described herein or as may be listed in any of the appended claims.
Yet further, the methods of the present invention do not require
use of the particular embodiments shown and described in the
present specification, but are equally applicable with any other
suitable structure, form and configuration of components.
[0069] The present invention does not require all of the above
components, features and processes. Any one or more of the above
components, features and processes may be employed in any suitable
configuration without inclusion of other such components, features
and processes. Further, while preferred embodiments of this
invention have been shown and described, many variations,
modifications and/or changes of the system, apparatus and methods
of the present invention, such as in the components, details of
construction and operation, arrangement of parts and/or methods of
use, are possible, contemplated by the patentee, within the scope
of the appended claims, and may be made and used by one of ordinary
skill in the art without departing from the spirit or teachings of
the invention and scope of appended claims. Moreover, the present
invention includes additional features, capabilities, functions,
methods, uses and applications that have not been specifically
addressed herein but are, or will become, apparent from the
description herein, the appended drawings and claims. Thus, all
matter herein set forth or shown in the accompanying drawings
should thus be interpreted as illustrative and not limiting.
Accordingly, the scope of the invention and the appended claims is
not limited to the embodiments described and shown herein.
* * * * *